This invention relates to corrugators, particularly, but not exclusively, chainless, for molding thermoplastic pipes, externally ribbed or corrugated.
Known chainless apparatus (U.S. Pats. Nos. 4,021,178 and 4,504,206) include two trains of moldblock halves circulating respectively in two endless paths containing a straight forward run wherein the halves cooperate with each other in the directions of their circulation and perpendicularly to the latter, to form a travelling mold for the thermoplastic pipe, a return run and two semi-circumferential guide tracks for transferring the halves between said runs.
The independent halves of the known apparatus cannot withstand the hydraulic pressure of molding acting to separate the halves in the direction of their circulation. That is why, such apparatus cannot be used successfully in the molding of externally ribbed pipes (described, for example, in U.S. Pat. No. 3,998,579 and in blow molding of extremely large corrugated pipes.